Micromachined Comb Capacitive Accelerometer Sticking Prevention
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Solution Overview
Problem
Existing micromachined comb capacitive accelerometers face issues with the mobile and fixed fingers sticking together due to electrical charge accumulation, leading to reduced production yield and malfunction, particularly after shocks or voltage application, which existing solutions like thick sacrificial layers and high-temperature processes are complex to implement.
Innovation Solution
The solution involves connecting the mobile and fixed fingers using beams etched directly into the substrate, increasing their rigidity and sensitivity, and using flexible rods to attach the mobile electrode to the substrate, while eliminating the need for a deposited sacrificial layer by etching and anchoring points, thus avoiding mechanical stresses and sticking issues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a thick sacrificial layer is used to prevent fingers from sticking, then the reliability is improved, but the device complexity and manufacturing difficulty increase
Solution Approach 1:
The patent removes the sacrificial layer entirely and replaces it with connecting beams etched directly in the substrate. This extraction of the harmful element (sacrificial layer) eliminates the sticking problem while simplifying the manufacturing process by removing the need for thick layer deposition and high-temperature processing.
Solution Approach 2:
The patent introduces connecting beams as intermediary structures etched in the substrate to mechanically link the fingers. These beams serve as mediators that provide structural support and prevent finger sticking without requiring sacrificial layers, thus improving reliability while reducing manufacturing complexity.
2Reliability
If a non-stressed layer is deposited to join fingers, then the reliability is improved, but the ease of manufacture deteriorates due to limited material choices and high-temperature requirements
Solution Approach 1:
The patent replaces the mechanical deposition process (requiring non-stressed layer deposition) with a direct etching process. This substitution eliminates the need for complex material deposition and high-temperature processing, making the manufacturing process simpler while maintaining structural integrity through the etched connecting beams.
Solution Approach 2:
The patent changes the manufacturing parameters from high-temperature deposition to standard etching processes. By altering the process parameters from mechanical deposition to chemical/physical etching, the patent achieves reliable finger connections without the constraints of material stress and temperature requirements.
3Ease of manufacture
If connecting beams are etched directly in the substrate, then the ease of manufacture is improved, but the rigidity of the finger ensemble may be reduced
Solution Approach 1:
The patent applies local quality by creating connecting beams with varying dimensions and positions throughout the substrate. The beams are strategically designed with different thicknesses and lengths at different locations to provide optimal rigidity where needed while maintaining ease of manufacture through direct etching. This localized optimization ensures structural strength without compromising manufacturing simplicity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enhances the rigidity and sensitivity of the accelerometer without increasing its size, eliminates the sticking problem, and simplifies the manufacturing process by using monocrystalline silicon connecting beams and anchoring points, improving production yield and reliability.
Implementation Method 1
under the effect of acceleration according to the axis of the mobile mass 6, the latter is displaced in the plane relative to the substrate 5
Implementation Method 2
This relative displacement produces a variation in the capacity between the mobile fingers 7 and the fixed fingers 8. The acceleration measurement is realised by the measurement of this variation in capacity.
Implementation Method 3
The mobile mass 6 is connected to the substrate 5 by a flexible rod 12 defining a return spring.
Data Source
AI summary
A comb capacitive accelerometer comprising a substrate, a mobile electrode relative to said substrate fitted with a plurality of mobile fingers, an electrode fixed relative to said substrate fitted with a plurality of fixed fingers, each of said mobile fingers being positioned between two contiguous fixed fingers so as to form a microstructure with interdigital combs. According to the invention the mobile fingers are connected to one another by at least a first connecting beam etched directly into the substrate, and/or the fixed fingers are connected to one another by at least a second connecting beam etched directly in the substrate.